1. Field of the Invention
The present invention relates to a radiation sensitive resin composition, and more specifically, to a radiation sensitive resin composition suitable for use as a chemically amplified resist.
2. Description of Background Art
In the field of microfabrication, as exemplified by the manufacturing of an integrated circuit device, development of a lithographic process capable of performing microfabrication with a 0.2 .mu.m or less line-width precision has been vigorously pursued in recent years to achieve higher integration.
To ensure microfabrication in the order of 0.2 .mu.m or less, the use of short wavelength radioactive rays is being studied. As such short wavelength radioactive rays, far ultraviolet rays, X-rays, and electron beams, typified by a bright-line spectrum of mercury-vapor light and an excimer laser, can be given. Of these, a KrF excimer laser (wavelength: 248 nm) and an ArF excimer laser (wavelength: 193 nm) are regarded as promising.
A number of compositions utilizing a chemical amplification effect of a component which has an acid-decomposable functional group and a component which generates an acid when irradiated with radioactive rays have been proposed as radiation-sensitive resin compositions applicable to irradiation by such excimer lasers. Such a composition is hereinafter called "a chemically amplified radiation sensitive composition" and such a component which generates an acid when irradiated with radioactive rays is hereinafter called "an acid generator".
For example, Japanese Patent Publication No. 27660/1990 discloses a chemically amplified radiation sensitive composition comprising a polymer having a t-butyl ester group of carboxylic acid or a t-butyl carbonate group of phenol and an acid generator. The t-butyl ester group or t-butyl carbonate group in the polymer dissociates by the action of the acid which is generated by irradiation of radioactive rays. As a consequence, the polymer has an acidic group consisting of a carboxyl group or phenolic hydroxyl group, which makes the irradiatied areas on the resist film easily soluble in an alkaline developer.
Most conventional chemically amplified radiation sensitive compositions contain a phenol-type base resin. When deep ultraviolet rays are used with such a resin, part of the deep ultraviolet rays is absorbed by the aromatic ring in the resin, so that a sufficient amount of the deep ultraviolet rays cannot reach the deepest part of the resist film. The irradiation dose is larger at the resist film surface than the resist film. As a consequence, in the case of positive working resists, the resist pattern after development which is smaller around the surface parts increases progressively toward the bottom. No sufficient resolution can be obtained. In addition, if a resist pattern after development provides a trapezoid section, no desired dimensional precision can be obtained in the subsequent etching and ion implantation steps. Unless the sectional configuration of the resist pattern is rectangular in the upper layer, the resist dissipates so fast by dry etching that it is difficult to control the etching conditions.
The configuration of resist pattern can be improved by increasing the transmittance of radioactive rays of the resist film. For example, a (meth)acrylate-type resin represented by poly (methyl methacrylate) exhibits a high transparency to deep ultraviolet rays. This type of resin is therefore ideal from the viewpoint of radioactive ray transmittance. Japanese Patent Application Laid-open No. 226461/1992, for example, discloses a chemically amplified radiation-sensitive resin composition comprising a methacrylate-based resin. This composition is excellent inasmuch as its performance of microfabrication is concerned. However, the composition has a drawback of a low dry etching resistance due to absence of an aromatic ring. It is difficult to perform etching with high-resolution.
In addition, a number of three or higher multi-component compositions in which high or low molecular weight additives are incorporated have been proposed as a means for improving performance of the resist comprising a chemically amplified radiation sensitive composition. However, the relationship between the radiation transmittance of resist films and the function of the additives in these compositions has not been completely clarified. In addition, these compositions do not necessarily satisfy an overall balance of important characteristics as a resist, such as dry etching resistance, pattern configuration, sensitivity, resolution, and the like. For instance, a resist composition disclosed in Japanese Patent Application Laid-open No. 15865/1997, which comprises a copolymer containing (meth)acrylate and (meth)acrylic acid as essential components, and acid generator, and androstane-17-alkyl carboxylate, has a difficulty in adequately controlling diffusion of acid in the resist film during formation of resist patterns, in spite of its high transparency to radioactive rays. The difficulty in controlling diffusion of acid not only results in unsatisfactory pattern configuration, sensitivity, and resolution, but also in poor dry etching resistance, insufficient developability, and impaired adhesive properties to substrates.
Adequate control of acid diffusion in resist films is very important for obtaining an excellent resist profile, particularly in the area where the fabricated pattern size is 0.20 .mu.m or less. Development of a radiation-sensitive resin composition which can effectively control acid diffusion has been desired from such a point of view.
An object of the present invention is therefore to provide a radiation-sensitive resin composition useful as a chemically amplified resist which is sensitive to reactive radioactive rays such as deep ultraviolet rays, typified by a KrF excimer laser or an ArF excimer laser, for example, exhibiting high transparency to radiation, superior dry-etching resistance, high resolution, and an excellent property balance such as pattern configuration and sensitivity.